JP2952939B2 - Method for forming metal wiring of semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a metal wiring of a semiconductor device in which a metal wiring is formed by electrolytic plating.

[Conventional technology]

7 (a), (b), (c) and (d) are cross-sectional views showing respective steps of a conventional example of a method for forming a metal wiring of a semiconductor device of this kind.

As shown in FIG. 7 (a), an insulating film 102 such as silicon oxide or silicon nitride is formed on a silicon substrate 101 by using a method such as a thermal oxidation method, a thermal nitridation method, a CVD method, or a sputter deposition method. Thickness of several thousand angstroms, followed by insulating film
Titanium, tungsten, molybdenum and alloys containing these, and an underlying metal film 103 which is a silicide or nitride of these metals are formed on the base layer 102 by a known method such as sputtering, reactive sputtering, or CVD. It is formed with a thickness of one hundred to several thousand angstroms, and a metal protective film 104 made of gold, platinum, palladium, rhodium, rhenium, or an alloy containing these elements is formed on the underlying metal film 103 by sputtering. It is formed with a thickness of 100 to 2000 angstroms. At this time, the base metal film 103 retains or improves the adhesion between the metal wiring and the insulating film 102 formed later by the electrolytic plating method, and improves the heat resistance, electromigration resistance, and stress migration resistance of the metal wiring. It is formed for the purpose of supplying a plating current to a plating film deposition portion at the time of electrolytic plating, and the metal protective film 104 prevents corrosion that easily occurs when the base metal film 103 and the plating solution come into direct contact at the time of electrolytic plating, It is formed for the purpose of improving the deposition property of the plating film during the electrolytic plating, stabilizing the supply of the plating current, and maintaining or improving the adhesion between the metal wiring formed by the electrolytic plating and the underlying metal film 103.

Subsequently, as shown in FIG. 7B, a thickness of several μm to several tens μm is formed on the metal protective film 104 by using a known PR method.
An m-th wiring forming mask film 105 is formed.

Further, the base metal film 103 and the metal protective film 104 are used as a cathode, and a metal electrode plate formed with a thickness of several thousand angstroms to several μm by plating or crimping of platinum on the surface of a mesh-shaped titanium plate is used as an anode. Solution containing ions of gold, copper, tin, lead, nickel, cobalt, palladium, etc., kept at a constant temperature in a range of ° C.
Alternatively, it is brought into contact with a plating solution composed of components to which a pH buffer, a brightener, a stabilizer, a flattening agent, etc. are added, and has a waveform such as a direct current, a rectangle, a sawtooth shape, a sine waveform between the positive and negative electrodes. By applying and energizing a bias of several hundred mV to several tens V, for example, as shown in FIG.
A plating film 106 made of copper, tin, lead, nickel, cobalt, palladium, or an alloy thereof is selectively formed only on a portion where the wiring forming mask film 105 is not present to a thickness of several thousand angstroms to several tens μm. .

Subsequently, as shown in FIG. 7D, the wiring forming mask film 105 is removed by a known method such as a wet method using an organic solvent or an ashing method using oxygen plasma.
Furthermore, using the plating film 106 as an etching mask,
Wet etching using an etching solution such as aqueous hydrogen peroxide, hydrofluoric acid, phosphoric acid, or ion milling using argon ions, dry etching using CF ₄ , SF ₆ , CCl ₄ , CHF ₃ or the like as an etching gas Unnecessary portions of the metal protective film 104 and the underlying metal film 103 are removed by a known technique such as that described above to form a metal wiring composed of the plating film 106, the metal protective film 104, and the underlying metal film 103.

[Problems to be solved by the invention]

The above-described conventional method for forming a metal wiring by electrolytic plating has the following disadvantages.

(1) When the bias applied at the time of electrolytic plating is DC or when the thickness of the wiring forming mask film is large, it is difficult to sufficiently diffuse metal ions in front of the contact interface between the plating object and the plating solution. As plating proceeds, the metal ion concentration decreases, the thickness and quality of the plating film tend to be non-uniform, and it is difficult to obtain stable electrical characteristics.

(2) When the bias applied at the time of electrolytic plating is a discontinuous type such as a rectangle, the phenomenon of (1) is less likely to occur,
When the wiring width is as fine as about 1 μm or less, the phenomenon (1) is apt to occur, so that the thickness and quality of the plating film are likely to be uneven, and it is difficult to obtain stable electric characteristics. Become.

An object of the present invention is to provide a method for forming a metal wiring of a semiconductor device which does not have the above-mentioned disadvantages.

[Means for solving the problem]

The method of forming a metal wiring of a semiconductor device according to the present invention is a method of forming a metal wiring of a semiconductor device, wherein a metal wiring is formed by electroplating on a portion of a semiconductor substrate which is not covered with a wiring forming mask, Contacting the negative and positive electrodes with a solution containing the ions of the metal used for the wiring material using the metal electrode as the anode, and applying an intermittent ultrasonic wave having a fixed period to the solution containing the metal ions, the plating solution or the object to be plated While the phase is different from the intermittent ultrasonic wave, and has a constant period, furthermore, a current having at least an intermittent waveform is applied between the cathode and the anode to perform electrolytic plating, and a step of forming a metal film. Forming a metal wiring by removing unnecessary metal portions.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

1 (a), 1 (b), 1 (c) and 1 (d) are cross-sectional views showing respective steps of a first embodiment of a method for forming a metal wiring of a semiconductor device according to the present invention, and FIGS. FIG. 3 is a waveform diagram showing an intermittent ultrasonic wave and an intermittent bias used in the embodiment of FIG. 1, respectively.

As shown in FIG. 1A, an insulating film 102 of silicon oxide, silicon nitride, or the like is formed on a silicon substrate 101 by using a method such as a thermal oxidation method, a thermal nitridation method, a CVD method, or a sputter deposition method. Thickness of several thousand angstroms, followed by insulating film
On 102, titanium, tungsten, molybdenum and alloys containing these and silicides of these metals, or a base metal film 103 which is a nitride, by a known method such as sputtering, reactive sputtering, or CVD, Formed with a thickness of several hundreds to several thousand angstroms, and further formed on the base metal film 103 by sputtering using a metal protective film 104 made of gold, platinum, palladium, rhodium, rhenium, or an alloy containing these elements. It is formed with a thickness of several hundred to 2,000 angstroms. At this time, the base metal film 103 retains or improves the adhesion between the metal wiring and the insulating film 102 formed later by the electrolytic plating method, and improves the heat resistance, electromigration resistance, and stress migration resistance of the metal wiring. The metal protective film 104 is formed for the purpose of supplying a plating current to a plating film deposition portion during electrolytic plating.
Is to prevent corrosion, which is likely to occur when the plating solution comes into direct contact with the underlying metal film 103 during electrolytic plating, to improve the deposition properties during electrolytic plating, to stabilize the supply of plating current, and to make the metal wiring and substrate formed by electrolytic plating. It is formed for the purpose of maintaining or improving the adhesion to the metal film 103 and the like.

Subsequently, as shown in FIG. 1 (b), a thickness of several μm to several tens μm is formed on the metal protective film 104 by using a known PR method.
An m-th wiring forming mask film 105 is formed. Further, the base metal film 103 and the metal protective film 104 are used as a cathode, and a metal electrode plate formed with a thickness of several thousand angstroms to several μm by plating or crimping of platinum on the surface of a mesh-like titanium plate is used as an anode. Consisting of, for example, sodium gold sulfate, sulfuric acid, sodium hypophosphite, and components added with a pH buffer, a brightener, a stabilizer, a leveling agent, etc., which are kept at a constant temperature within a range of ℃. Contact with the plating solution.

Subsequently, the step shown in FIG. 1 (c) is performed. The gold plating solution has a waveform as shown in FIG.
z, while applying intermittent ultrasonic waves of several watts to several hundred watts, apply an intermittent bias of several hundred mV to several tens of volts as shown in FIG. The formed plating film 106 is selectively formed only on the metal protective film 104 where the wiring forming mask film 105 does not exist, with a thickness of several thousand angstroms to several tens μm. At the end of the intermittent bias application in the plating film deposition process, the metal ion concentration in front of the interface between the plating object and the plating solution is low.

In the conventional electroplating method using intermittent bias application, the gold ion concentration in front of the object to be plated can be recovered when the bias application is suspended, but the fine part and the thick mask film for wiring formation have high aspect ratio. In this case, it is difficult to obtain the effect because the plating solution is hardly agitated. However, in this embodiment, since the intermittent ultrasonic wave is applied immediately after the completion of the application of the bias, the plating solution is sufficiently agitated by the effect of the ultrasonic wave even in a fine portion and a high aspect ratio portion. Therefore, the recovery of the gold ion concentration in front of the interface is rapid, and a uniform diffusion double layer can be formed, and a plating film having high uniformity in film thickness and film quality can be formed.
At this time, the frequency and the intermittent period of the intermittent ultrasonic wave to be applied are
Since the output depends on the bias application conditions during plating and the type of metal ions in the plating solution, the output varies depending on the plating equipment, the shape and size of the plating object, and the contact state between the plating solution and the plating object. Although it is necessary to set the optimum conditions for both, the output is not required to generate bubbles in the plating solution due to the cavitation phenomenon.

Subsequently, as shown in FIG. 1D, the wiring forming mask film 105 is removed by a known method such as a wet method using an organic solvent or an ashing method using oxygen plasma, and the plating film 106 is further formed. Aqua regia, used as an etching mask
Wet etching using hydrogen peroxide, hydrofluoric acid, phosphoric acid, etc. as an etching solution, ion milling using argon ions, or using CF ₄ , SF ₆ , CCl ₄ , CHF ₃ etc. as an etching gas An unnecessary portion of the metal protective film 104 and the underlying metal film 103 is removed by a known method such as a dry etching method to remove the plating film 106, the metal protective film 104, and the underlying metal film 103.
A metal wiring is formed.

In the present embodiment, the supply of the plating current does not necessarily have to be performed from the front side of the silicon substrate, and a conductive layer having a structure that allows electrons to move from the back side to the front side is formed on the back side of the silicon substrate. It is also possible to perform plating by supplying a current to the underlying metal film on the surface.

The method for forming a metal wiring of a semiconductor device described in this embodiment is applicable regardless of the type of the semiconductor device such as moss or bipolar as long as it has a structure capable of supplying a current to a metal film on a silicon substrate. Needless to say.

4 (a), (b), (c) and (d) are cross-sectional views showing respective steps of the second embodiment of the present invention, and FIGS. 5 and 6 are each an embodiment of FIG. FIG. 6 is a waveform diagram showing intermittent ultrasonic waves and intermittent bias used in the method.

As shown in FIG. 4A, an insulating film 10 is formed on a silicon substrate 101 by using the same method and material as in the first embodiment.
2. Each of the base metal film 103 and the metal protection film 104 is formed with the same thickness as that of the first embodiment.

Next, as shown in FIG. 4B, a mask film for wiring formation
105 is formed in the same manner as in the first embodiment. Further, the substrate metal film 103 and the metal protective film 104 are used as a cathode, and a metal electrode plate formed in the same manner as in the first embodiment is used as an anode.
Consisting of, for example, copper sulfate, sulfuric acid, sodium hypophosphite and a component obtained by adding a pH buffer, a brightener, a stabilizer, a leveling agent, etc., which are kept at an appropriate temperature in the range of 0 ° C. Contact with a copper plating solution.

Subsequently, the step shown in FIG. 4 (c) is performed. The copper plating solution has a waveform as shown in FIG.
z, intermittent bias of several hundred mV to several tens of volts as shown in Fig. 6 is applied and energized between the negative and positive electrodes while applying intermittent ultrasonic waves of output several W to several hundred W, and composed of copper. The plating film 107 to be formed is selectively formed only on the metal protective film 104 where the wiring forming mask film 105 does not exist, with a thickness of several thousand angstroms to several tens μm.

In this embodiment as well, since the intermittent ultrasonic wave is applied immediately before the application of the bias, the stirring of the plating solution is always sufficiently performed by the effect of the ultrasonic wave even in a fine portion or a pattern having a high aspect ratio. Electroplating can be performed in a state of high uniformity of the metal ion concentration immediately after the plating. Therefore, a uniform diffusion double layer is formed,
Plating film with high film quality uniformity can be formed. At this time, the conditions of the intermittent ultrasonic wave and the bias to be applied are as described in the first embodiment.

Subsequently, as shown in FIG. 4D, the wiring forming mask film 105 is removed by a known method such as a wet method using an organic solvent or an ashing method using oxygen plasma, and the plating film 106 is further formed. Aqua regia, used as an etching mask
Wet etching using hydrogen peroxide, hydrofluoric acid, phosphoric acid, etc. as an etching solution, ion milling using argon ions, or using CF ₄ , SF ₆ , CCl ₄ , CHF ₃ etc. as an etching gas An unnecessary portion of the metal protective film 104 and the underlying metal film 103 is removed by a known method such as a dry etching method to remove the plating film 106, the metal protective film 104, and the underlying metal film 103.
A metal wiring is formed.

〔The invention's effect〕

As described above, according to the present invention, fineness is achieved by applying intermittent ultrasonic waves having a phase different from that of the intermittent bias to the plating solution or the object to be plated while the intermittent bias applied when performing electrolytic plating is stopped. Easy to stir near the interface between the plating object and the plating solution even in complicated wiring patterns and patterns with a high aspect ratio, and uniformity of film thickness and film quality compared to the conventional plating method using intermittent bias. Therefore, there is an effect that a fine metal wiring having stable electric characteristics can be formed.

[Brief description of the drawings]

1 (a), 1 (b), 1 (c) and 1 (d) are cross-sectional views showing respective steps of a first embodiment of a method for forming a metal wiring of a semiconductor device according to the present invention, and FIGS. 4 is a waveform diagram showing an intermittent ultrasonic wave and an intermittent bias used in the embodiment of FIG. 1, respectively. FIGS. 4 (a), (b), (c) and (d) are second embodiments of the present invention. Sectional views showing the steps of FIG.
4 is a waveform diagram showing the intermittent ultrasonic wave and the intermittent bias used in the embodiment of FIG. 4, and FIG. 7 is a sectional view showing each step of the conventional example. 101: silicon substrate, 102: insulating film, 103: base metal film, 104: metal protective film, 105: mask film for wiring formation, 106: plating film.

Claims (1)

(57) [Claims] 1. A metal wiring forming method for a semiconductor device, wherein a metal wiring is formed by electroplating on a portion of a semiconductor substrate which is not covered by a wiring forming mask, wherein the semiconductor substrate is used as a cathode and the metal electrode is used as an anode. Contacting the negative and positive electrodes with a solution containing metal ions to be used for, and applying an intermittent ultrasonic wave having a fixed period to the solution containing the metal ions or the object to be plated, while intermittently applying a phase to the intermittent ultrasonic wave. A step of forming a metal film by passing a current having at least an intermittent waveform between the cathode and the anode, and forming a metal film, and then removing unnecessary metal portions. Forming a metal wiring by performing the method.